PROJECT SUMMARY The link between iAs exposure and type-2 diabetes (T2D) is supported by strong data from epidemiologic and laboratory studies. However, the diabetogenic effects of iAs exposure during specific developmental windows (e.g., prenatal or postnatal) and the underlying mechanisms are poorly understood. The role of iAs metabolism as a key factor modifying the effects of iAs at these exposure windows is also unclear. This project will use a unique animal model and a transdisciplinary design to address these critical knowledge gaps. Our hypothesis is that both prenatal and postnatal exposures to iAs will result in diabetes, but the phenotypes and underlying mechanisms will be different and will depend, in part, on the efficiency of iAs metabolism. We anticipate that prenatal exposure alone will result in epigenetic reprograming of genes that regulate ?-cell and insulin function, and that were differentially methylated by iAs exposure in adults and newborns in our cohorts in Mexico. We expect that postnatal exposure will be tied primarily to inhibition of insulin secretion or insulin signaling, and that these effects will correlate with concentrations of iAs or its metabolites in the pancreas in the glucose metabolizing tissues. Dietary supplementation with folate or vitamin B12, the donors or methyl groups for iAs methylation, and knockout of As3mt that catalyzes iAs methylation are expected to modify the diabetogenic effects of both prenatal and postnatal exposure to iAs. The specific aims are: 1. Compare the diabetic phenotypes associated with pre- or postnatal exposure to iAs. We will examine fasting glycemia, glucose tolerance, insulin resistance and ?-cell function in male and female wild-type (WT) C57BL/6 mice exposed to iAs in drinking water prenatally or after birth. We will identify metabolic dysfunction associated with each exposure window. 2. Identify mechanisms underlying the diabetogenic effects of pre- or postnatal exposure to iAs. We will assess pancreatic islet integrity and function and insulin signaling in tissues of WT mice exposed pre- or postnatally to iAs in Aim 1. We will also examine the CpG methylation and expression of twelve T2D- associated genes that were differentially methylated by iAs exposure in our population studies. 3. Determine the role of iAs metabolism as a modulator of the diabetogenic effects of pre- and postnatal iAs exposure. We will examine diabetic phenotypes and underlying mechanisms in mice in which the capacity to metabolize iAs will be modified by folate/B12 supplementation or by As3mt knockout. This project will be the first to compare the diabetogenic effects of pre- and postnatal iAs exposures and to determine the role of iAs metabolism as a modifier of these effects. Results will inform design and aims of the current and future population studies carried out by both PI's (Drs. Styblo and Fry), and will also help to optimize the treatment and prevention strategies for iAs-associated T2D.